Clinton held a rally Monday evening in Kissimmee, and Seddique Mateen, whose son shot and killed 49 people and injured 53 others inside the Pulse nightclub in June, was spotted in the crowd directly behind the candidate.

Clinton focused on the economy during her speech, but she also discussed the mass shooting.

"I know how many people, family members, loved ones and friends are still grieving," Clinton said.

Mateen was confronted by a reporter as he left the rally.

"What went into your decision about going to this event right near Orlando, where this Pulse nightclub shooting happened?" the reporter said.

"I spoke a lot about that," Mateen said. "And I wish my son joined the Army and fought ISIS and destroyed ISIS. That would be much better."

A campaign official said Tuesday the Clinton did not know Mateen was at the rally.

"The rally was a 3,000-person, open-door event for the public. This individual wasn't invited as a guest, and the campaign was unaware of his attendance until after the event," the Clinton campaign said.

Mateen's son, Omar Mateen, was shot and killed by police inside the nightclub.